1. Field of the Invention
The present invention relates generally to the production of superconducting materials and more specifically to the production of superconducting materials in bulk form.
2. Description of the Prior Art
Superconducting materials in bulk form are used as precursors in the fabrication of superconducting films and wires. Because the superconductivity of a film or thin wire can be no better than that of the bulk material from which it was fabricated, persons in the art have sought to produce bulk materials having maximum superconductivity.
The need for bulk materials of high superconductivity increased with the discovery of high T.sub.c superconducting materials. Most of the high T.sub.c superconductors presently known are sintered polycrystalline materials. High current densities have not yet been achieved in sintered polycrystalline material because of extensive porosity. While Hot Isostatic Pressing has produced bulk superconducting materials with near-theoretical density, prior art attempts to produce superconductor materials directly from the melt have been limited, especially in the recently discovered Bi-Sr-Ca-Cu-O system, a member of the perovskite oxide family. Thus, although the art has recognized the need for a simple and convenient method of producing superconductor materials in bulk form, that need went unfulfilled.
Although it is believed not to be prior art with respect to the present invention (based upon the presently known evidence of dates of conception and reduction to practice) the independent work of Das et al (done while employed by the assignee) is similar to that of the present invention. The work of Das et al was published as Journal of Superconductivity, Vol. 2, No. 2, (1989) (incorporated herein by reference). Because information disclosed in the Das et al paper may provide useful insights into the present invention, review of that paper is strongly recommended. In addition to providing information concerning practice of the present invention, the Das et al paper also describes the failures of the prior art to successfully cast various superconductors from the melt.